Magnetic tunnel junctions can be used as memory elements in magnetic random access memory (“MRAM”) devices. MRAM has lower power consumption than short-term memory such as DRAM, SRAM and Flash memory. MRAM can perform read and write operations much faster (by orders of magnitude) than conventional long-term storage devices such as hard drives. In addition, MRAM is more compact and consumes less power than hard drives.
Magnetic tunnel junctions can be used as magnetic sensors in read heads of hard disk drives. The magnetic tunnel junctions can generate stronger readback signals than giant magnetoresistive devices and other conventional devices.
A conventional magnetic tunnel junction includes an antiferromagnetic (AF) pinning layer, a pinned ferromagnetic (FM) layer formed on the pinning layer, an insulating tunnel barrier formed on the pinned ferromagnetic layer, and a free ferromagnetic layer formed on the insulating tunnel barrier. Relative orientation and magnitude of spin polarization of the ferromagnetic layers determine the resistance of the magnetic tunnel junction.
In this conventional bottom-pinned magnetic tunnel junction, a lattice mismatch can occur between the AF pinning and pinned FM layers. This lattice mismatch increases the roughness on an upper surface of the pinning layer. The increased roughness, in turn, increases ferromagnetic (FM) coupling between the pinned and free layers.
The FM coupling between the pinned and free layers can cause problems in magnetic tunnel junctions. In read heads, the FM coupling can cause readback signal distortion. Bias techniques can be used to correct the signal distortion. However, the bias techniques tend to be complex to implement and costly to fabricate.
In magnetic memory elements, the FM coupling can render magnetic tunnel junctions unusable. Unusable magnetic tunnel junctions can reduce MRAM performance, increase fabrication cost, and increase the complexity of read circuits.
It would be desirable to reduce the FM coupling.